You're going to have deliverability issues with Gmail no matter what if you roll your own. I had ran my own mail server with SPF/DKIM/DMARC/etc. for 15+ years, all setup correctly and still had no guarantee that messages would inbox. I finally gave in and switched to an offshore 3rd party service for hosted emails to keep the "I wonder if that important email actually got delivered to their hosted Gapps" at bay.